Supercritical CO₂ extraction of onion seed oil and its synergistic effect with gentamicin against bacterial strains

Antibiotic resistance represents a major global health challenge, requiring innovative strategies to enhance the effectiveness of existing antimicrobial agents. In this study, onion seed oil was extracted using supercritical CO₂ and evaluated for its potential to improve the antibacterial activity of the antibiotic gentamicin. The oil was characterized through physicochemical analyses, including FTIR spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Antibacterial activity was tested against Staphylococcus aureus and Escherichia coli using the disk diffusion method. The results demonstrated that onion seed oil exhibited significant antibacterial activity and enhanced the efficacy of gentamicin when used in combination. The synergistic interaction increased inhibition zone diameters by up to 20.4% for S. aureus and 22.95% for E. coli, even at low extract concentrations. These findings suggest that supercritical CO₂-extracted onion seed oil may serve as a promising natural adjuvant to improve antibiotic performance and combat bacterial resistance.